1. Field of the Invention
The present invention relates to the field of the three-dimensional digitization, in real time and without contact, of objects industrially manufactured or designed in research laboratories, and relates in particular to the so-called “chromatic confocal” optical apparatuses.
More specifically, the invention relates to a chromatic converter for altimetry which generates a real image of the measurement field containing a sample, by converting the local height of its surface into wavelength.
The device comprises a polychromatic light source and an optical device intended to transform the light emitted by the source into numerous parallel polarized beams provided with essentially axial chromatism. The reflection of these beams on the sample to be studied is then analyzed by an analysis device in order to know the local height of the surface of the sample.
2. Description of Related Art
Devices that make it possible to know the height of a surface have already been disclosed, for example in the patent EP 0950168B1. The apparatus described digitizes slices of the surface of a sample, then performs a three-dimensional reconstruction of the surface using computer means. For this, the sample is lit by a chromatic beam, and placed on a plate that can be moved horizontally along x and y axes. For a given y position, the apparatus measures the wavelength reflected by the surface for a series of x coordinates, which makes it possible to deduce there from the height z of the sample by virtue of the chromatic coding.
The major drawback of this analysis technique lies in the time it takes to digitize an image, which is very long. This is due to two factors: (i) the measurement which is performed point-by-point, and (ii) the plate which has to be moved during acquisitions.
The chromatic confocal device presented in the patent application FR 2950441A1 makes it possible to measure the height of a surface more quickly.
For this, a number of independent measurement pathways simultaneously determine the height of a number of points of the surface, such that a fraction of the observation zone is probed at one time.
More specifically, each beam reflected by a point of the surface is scattered by a spectral analysis device, in such a way that each spectrum obtained occupies all or part of a row of pixels of a photodetector. The number of points of the surface that can be analyzed simultaneously is therefore limited.
As an example, the holder of this patent specifies that the device makes it possible to divide up a 2048-pixel photoelectric detector between 10 measurement pathways.
To obtain the entire measurement of the observation zone, an internal scanning device is added to the apparatus. This device consists, for example, of a rotating mirror which deflects the beams from the measurement pathways to different points of the surface of the sample to be studied. By virtue of the internal scanning device, the acquisitions are performed without moving the sample.
This internal scanning method in a confocal device makes it possible to enhance the speed of acquisition of the measurements, but insufficiently.
Furthermore, the fact that each measurement pathway is independent creates a significant increase in the cost of the apparatus, because the optical elements and the spectral analysis devices are multiplied.
Moreover, the juxtaposing of the measurement pathways notably increases the size of the machine. To limit this drawback, the apparatus is divided up into two blocks linked by optical fibers in order to have a measurement head of reasonable dimensions, but this does nothing to resolve the problem linked to the overall bulk of the device.
It appears from the above that the current systems are ill-suited to industrial constraints, whether in terms of cost, bulk, and above all in terms of speed of analysis of the samples studied.
The patent application FR 2707018 A1 discloses an enhanced three-dimensional digitization device that makes it possible to cover an extended observation zone rapidly. More specifically, this device comprises a disk pierced with a multitude of holes and driven in rotation to create and displace secondary light sources, from a single light source, in order to scan all of the observation zone.